The present invention relates generally to electronic devices. More particularly, the present invention relates to interconnection of electronic devices at carrier frequencies in a range from a few gigahertz to several hundreds of terahertz, and more specifically to terahertz interconnection of electronic devices.
Increased amounts and speed of data transfer in communication and computing systems pose a challenge to the current state of device technology. Large quantities of information must be transferred quickly across distances ranging from very short distances, from between chips as well as between boards containing chips, to longer distances between racks of devices, very short reach (VSR)/optical Ethernet and beyond. Even with the development of high-speed communications switches and routers, the data must be taken in and out of such high-speed devices at compatibly high rates in order for the entire system to function efficiently.
Radio frequency (RF) inter-chip and intra-chip connections have been developed as a possible way of transferring data within and between chips. However, RF interconnects use large antennae and/or waveguides on or connected to chips, thus requiring valuable on-clip and device “real estate.” RF interconnects are limited in data transfer speed due to the use of radio frequencies. Furthermore, It is submitted that the design and manufacture of such RF lines for high signal frequencies is an expensive part of prior art RF interconnection design.
Other researchers have suggested the use of optical signals as an alternative to electrical signals in providing inter- and intra-chip connections.1 For instance, parallel fiber-optic interconnects which are edge-connected to semiconductor devices have been developed for use within systems with a large number of electronic components (e.g., computers).2 Although optical interconnect technology promises the possibility of higher rate data transfer than electrical interconnects, optical interconnect technology, as heretofore suggested, is still cost prohibitive in comparison. There is potentially a huge market for high speed interconnect arrangements because all desktop computers and local area networks would benefit from the use of high speed interconnects between components on chips, between chips, etc.
Currently, electrical interconnects are generally used in communication and computing systems for power and data signal distribution, such as in bus lines, etc. Electrical interconnects, however, require hardwired connections such as, for example, lithographed lead lines on a chip, wire bonds from the chip to a chip package, pins leading from inside the package to a circuit board, printed circuit board wiring, edge connectors from circuit board to other boards, input/output (I/O) devices, data storage devices, and others. Such hardwired connections add parasitic capacitance, inductance, and resistance, which seriously degrade data transmission at high data bandwidths. Thus, the cost and performance limitations of electrical interconnects are compounded as circuits are made to operate at increasingly high frequencies. At high frequencies, electrical interconnects are limited in connection distance and require large amounts of power as well as signal reconditioning. Applicants submit that there are at least two issues contributing to this problem. First issue is the relative change in material properties, such as refractive index and electromagnetic radiation propagation speed, over the bandwidth of the signal. A second, and perhaps more significant, issue is the relative difference in wavelength over the bandwidth of the signal. For example, if the signal bandwidth is centered at zero frequency (i.e., DC), then the wavelength of different signal components may range from infinity (for the DC components) to, for instance, centimeters for components at tens of gigahertz. This enormous range in wavelength makes it difficult to design electrical transmission paths which will work efficiently over the entire bandwidth range.
In addition to the aforementioned RF inter- and intra-chip interconnects, other wireless interconnects at other frequencies have also been suggested. For example, wireless data communications link between circuit components using GaAs-based MIMIC transmit/receive integrated circuit devices, operating at high-bandwidth millimeter-wave frequencies, coupled to corresponding circuit components, such as digital processing units (or CPUs) have been disclosed by Metze in U.S. Pat. No. 5,754,948 (hereinafter, Metze). It is submitted, however, that GaAs-based MIMICs are complex devices which require expensive epitaxial growth techniques in the fabrication. Applicants submit that epitaxial growth techniques are expensive and severely limit the integration of devices with different epitaxial layer structures. Also, the disclosure of Metze is confined to millimeter-wave frequencies; specifically, the transmit/receive circuit of Metze is described as preferably operating:                at frequency ranges above 35 GHz, and most preferably at frequencies between 60 GHz and 94 GHz . . . other frequencies may be utilized and still fall within the standard I.E.E.E. definition of “millimeter-wave” for purposes of this invention. (Metze, column 5 lines 25–32)Regarding the “standard I.E.E.E. definition of ‘millimeter-wave’” as referred to by Metze, according to the IEEE Virtual Museum website, the millimeter wave region is generally considered to correspond to 30 GHz to 300 GHz.3         
As another example of wireless interconnects, in U.S. Pat. No. 5,056,111, Duling, III, et al. (hereinafter Duling) discloses a communication system for transmitting and receiving terahertz signals, which involves the generation of sub-picosecond (i.e., terahertz) pulses for transmission of data. However, Applicants submit that ultrashort pulse generation, such as that disclosed in Duling, require complex systems such as femtosecond lasers that are impractical to use as a replacement for local electrical interconnects. As will be described at appropriate points below, the present invention recognizes certain problems with both the electrical interconnects and wireless interconnection schemes which are thought to be unresolved by the prior art.
As will be seen hereinafter, the present invention provides a significant improvement over the prior art as discussed above by virtue of its ability to provide the increased performance while, at the same time, having significant advantages in its manufacturability. This assertion is true for electromagnetic devices generally, which take advantage of the present invention, as well as data communication and computing devices in particular.